This invention relates to methods for inhibiting conception in mammals, especially human females, and to formulations for use in such methods. More particularly, the present invention is directed to contraceptive methods and preparations for use therein effective for extended periods of time.
Gonadotropin releasing hormone (GnRH), also known as luteinizing hormone releasing hormone (LHRH), produced by the hypothalamus controls the secretion of follicle stimulating hormone (FSH) and luteinizing hormone (LH) by the pituitary and thence gonadal steroid hormone production. Potent synthetic agonists of GnRH administered to premenopausal women have been shown to produce a transient rise in FSH/LH release followed by a sustained suppression. Immediately after GnRH agonists became available in the late 1970s, a number of approaches to the use of a GnRH agonist as a contraceptive were explored. Among these approaches, inhibition of ovulation by the chronic administration of GnRH agonists appeared to offer the greatest potential. It was hoped that GnRH agonists would form the basis of an improved method of contraception by offering greater convenience, increased effectiveness or fewer side effects than is the case with combination-type oral contraceptives (COCs).
Inhibition of ovulation by GnRH agonists has been found, as expected, to be dose-related. When administered in a dose just high enough to ensure anovulation, the ovaries may continue to produce estrogen. This is an unstable situation, with different women having widely varying serum estrogen levels. There has also been concern that endometrial hyperplasia would occur in some women, while in others there would be periods of hypoestrogenemia with unacceptable vasomotor symptoms and probably loss of bone mineral content.
"High-dose" GnRH agonists have been observed to uniformly reduce serum estradiol and serum progesterone to oophorectomized levels. The development of "high dose" depot formulations of GnRH agonists permits sustained inhibition of ovulation and suppression of ovarian steroid production, as well as improved ease of drug administration. The treatment is reversible; in a study of 50 patients, recovery of menstrual function occurred on average at 87 days (range 44-126 days) following 6-8 months treatment with the GnRH agonist tryptorelin [Zorn, J.-R. et al., Fertil.Steril. 53:401-06 (1990)]. Other depot formulations of GnRH agonists produce similar sex-steroid suppression including decapeptyl [George, M. et al., Int. J. Fertil. 34:19-24 (1989)], goserelin [Kaufman, M. et al., J. Clin. Oncol. 7:1113-19 (1989)]and buserelin [Donnez, J. et al., Fertil. Steril. 51:947-50 (1989)].
In spite of their clear effectiveness as contraceptive agents, side effects attendant to the use of "high-dose" GnRH agonists for prevention of pregnancy has prevented their general adoption. Common side effects reported to occur in depot GnRH agonists in premenopausal patients include: hot flashes, vaginal dryness, irregular vaginal bleeding and fatigue. Additional side effects that have been reported in some patients receiving GnRH agonists include: sweating, headache, depression, lability in mood, nausea and/or vomiting, nervousness, insomnia, pollakisuria, weight gain, sleepiness, dizziness, decreased libido and mild breast tenderness or swelling.
A recent review article reflects current thinking about GnRH and its analogues (Conn, P. M. and Crowley, Jr., W. F., "Gonadotropin-Releasing Hormone and Its Analogues," N. Enol. J. Med. 324:93-103 (1991)). The authors note at pages 96-97 that "whether to supplement GnRH-agonist analogues with sex steroids is a complex decision"; they propose estrogen replacement followed by the administration of a progestational agent "at physiologic doses and in a physiologic (i.e., sequential) pattern."
U.S. Pat. No. 4,762,717 to Crowley, Jr., the entire disclosure of which is hereby incorporated by reference, is based on the above-noted assumption that administration of a progestational agent should be effected in a sequential pattern so as to mimic the phases of the menstrual cycle. The patent describes contraceptive methods for female animals using luteinizing hormone releasing hormone (LHRH) compositions in combination with sex steroids. The patent calls for administering LHRH (or analogs, agonists or antagonists thereof) in a first delivery system combined with continuous administration of an effective amount of estrogenic steroids during the "follicular phase" of the menstrual cycle beginning at the onset of "normal menses". A second delivery system is administered during the "luteal phase" of the menstrual cycle until the onset of "normal menses". The second delivery system comprises the LHRH/estrogenic steroid combination and additionally provides an effective dosage of a progestational steroid.
This administration sequence is designed to mimic the physiological secretion o steroids in the menstrual cycle. As a consequence, each delivery system is effective for a period of only about two weeks (corresponding to the typical length of each of the follicular and luteal phases, according to the designation of Crowley). The progestational steroid according to Crowley is administered for fully half the time of the treatment program (i.e., throughout the time interval when the second delivery system is in use).
The approach of Crowley is clearly unacceptable when considered in light of current knowledge about the long-term effects of administering the components thereof for the periods of time specified. The proposed level of estrogen administration (i.e., to achieve an estradiol concentration of about 50 to about 140 pg/ml for a human female) in the two delivery system approach of Crowley is unnecessarily high and the proposed duration of progestogen use unnecessarily lengthy. Epidemiologic case-control studies of postmenopausal breast cancer risk and estrogen replacement therapy (ERT) using population controls suggest that increased exposure to exogenous estrogen leads to an increased risk of breast cancer in a dose-dependent fashion. Moreover, administration of progestational steroid for about two weeks of every approximately 28-day treatment cycle was associated with unacceptable risks to the patient in a recent epidemiological study [Bergkvist, L. et al., N. Engl. J. Med. 321:293-97 (1989)]; the study suggests that the addition of progestogen during the latter half of the 28-day ERT cycle may double the risk associated with use of estrogen alone.
Pike, M. C. et al., Br. J. Cancer 60:142-48 (1989), the entire disclosure of which is also hereby incorporated by reference, have proposed a contraceptive regimen in which "high-dose" LHRH agonist treatment is coupled with estrogen replacement therapy (ERT), specifically 0.625 mg of conjugated equine estrogens for 21 days in each 28-day treatment cycle. The administration of a progestational steroid is proposed to be limited to a 10-16 day interval every three or four cycles. It is now clear that the 7-day period in each treatment cycle when ERT is not provided would be associated in many patients with symptoms of estrogen withdrawal, such as hot flushes. Moreover, a negative calcium balance could develop during the period of hypoestrogenemia with the possibility of resultant osteoporosis. Finally, blood cholesterol levels would likely be adversely affected during that time. Therefore, it is unlikely that the specific regimen proposed by Pike et al. would be found acceptable.
It is an object of the present invention to provide a contraceptive regimen which would obviate the problems attendant to the use of existing methods of birth control, while at the same time reducing the risk of adverse consequences associated with the heretofore known methods.